It has long been known to use guidewires for guiding catheters through body lumens for various medical procedures. One application in which such guidewires are typically used is in the percutaneous delivery of a catheter into the vascular system. The guidewire is a long flexible metal wire which may be inserted into the body percutaneously and advanced through the vascular system to the desired location. The guidewire may then be used as a vehicle for transporting an accompanying catheter to the given location.
In order to negotiate a tortuous path through the vascular system and to avoid obstacles during insertion, guidewires may include a curved flexible distal tip which can adapt itself to the shape of the blood vessel so that it can be advanced through such curved vessel without injuring the walls of the vessel. However, it is also important for the guidewire to exhibit sufficient rigidity such that the guidewire can be pushed forward without buckling or kinking. Further, proper advancement of the guidewire requires that the guidewire exhibit steerability. That is, the guidewire must be capable of being rotated so as to traverse curved portions of the vessel. Accordingly, the guidewire must also exhibit substantial torsional rigidity so that rotation of a proximate shaft portion causes corresponding rotation of the distal tip.
Guidewires of the type described herein are especially useful in procedures such as percutaneous transluminal coronary angioplasty (PTCA) and percutaneous transluminal angioplasty (PTA). In these procedures, the guidewires may be used to guide a balloon dilatation catheter to a stenosis in the blood vessel where upon the balloon of the guidewire is directed to the stenosis and the balloon is inflated thereby breaking apart the stenosed area of the vessel. Many guidewires, especially those used for PTCA procedures, are of relatively small diameter having an outer diameter not exceeding 0.018". The maximum diameter of a guidewire is limited by the internal diameter of the guidewire lumen in the balloon dilation catheter and by the vessel through which it must traverse.
The art has seen many attempts to provide guidewires which combine a relatively rigid shaft portion exhibiting substantial torsional rigidity and steerability and a flexible distal tip portion which facilitates traverse of the guidewire through the vascular system.
U.S. Pat. No. 4,925,445 describes a guidewire including a shaft portion and a distal tip portion which are formed from a superelastic TiNi alloy. The superelastic TiNi material enhances bendability and kink resistance of the guidewire. The entire guidewire may include a plastic coating thereover which enhances the ability of the guidewire to safely traverse the vascular system. The plastic coating may also contain an x-ray contrast medium such as metal particles therein which enhances the radiopacity of the guidewire.
However it has been found that with small sized guidewires such as those used for PCTA procedures, it is difficult to place a uniformly thin plastic coating thereover or if the guidewire is coated, the shaft may not exhibit the desired stiffness. Further, it is desirable in many instances to limit the plastic coating to the tip portion alone. This type of construction, with a coated tip portion and an uncoated shaft portion, helps transmit torque directly from the shaft portion to the tip portion resulting in enhanced steerability and maximum shaft stiffness. However, it is extremely difficult to coat only the flexible, thin distal tip portion of the guidewire. Attempts to coat the entire guidewire and selectively remove the coating from the shaft portion result in the coated tip portion having a larger diameter than the shaft portion.
It is also known to employ low friction hydrophilic coatings over guidewires. The hydrophilic coating increases the lubricity of the guidewire and allows the guidewire to more easily be maneuvered through tortuous areas of the vascular system. Examples of hydrophilic coatings in guidewire applications are found in U.S. Pat. Nos. 5,129,890 and 5,213,111.
However, none of the prior art techniques has been found to be suitable in providing a plastic coating at the distal tip of the guidewire where the overall diameter of the guidewire is not increased, so that the guidewire may still be used in locations requiring small diameters and allowing the guidewire to be passed through catheters having an internal luminal diameter which closely approximates the diameter of the shaft.